The present invention relates to a vehicle occupant safety systems, and more particularly, to a vehicle occupant proximity sensor for use with a vehicle occupant safety system.
Vehicle occupant safety systems that are activated in response to a vehicle crash for purpose of mitigating occupant injury are well known in the art. A vehicle may contain automatic safety restraint actuators such as front and side air bags, seat belt pretensioners, and deployable knee bolsters. The occupant protection system may further include a collision/crash sensor for sensing the occurrence of a vehicle crash and for providing an electrical signal indicative of the crash severity.
Several known occupant protection systems include an occupant position sensor that senses the position of the occupant with respect to an associated inflatable protection module. The occupant position sensor for such a system could be an ultrasonic sensor, an infrared sensor, and a capacitive sensor, and/or a weight sensor. A controller, which is connected to the sensors, controls the inflatable protection module in response to the sensed position of the occupant. In response to the sensed occupant position, one or more deployment aspects of the air bag may be adjusted. A protection system with adjustable aspects of deployment is commonly referred to as an xe2x80x9cadaptivexe2x80x9d protection system. Specifically, if the occupant is positioned in a position such that deploying the air bag will not enhance protection of the occupant, it may be desirable to suppress actuation of the occupant protection module. An occupant who is very near the protection module is referred to as being within an occupant out-of-position zone. Deploying the air bag for an occupant who is within the occupant out-of-position zone may not enhance protection of the occupant.
In any case the determination of occupant""s position is an important part of adaptive occupant protection system. There are several types of proximity sensors, such as ultrasonic sensor, a video sensor, a capacitive sensor, and an infrared sensor. Different obstacles such as a map, a book, or a newspaper could occlude signals from ultrasonic and video sensors. A lighter or cigarette could blind an infrared sensor. Existing capacitive sensors rely on the strength of the electric field to determine proximity (i.e. dash mounted capacitive sensor). This makes the sensor susceptible to being fooled if the strength of the electric field is blocked. A system that relies on the strength of the electric field may be inaccurate if a portion of the signal is lost. Furthermore, existing sensors are also complex and expensive.
This invention is based on a simple factxe2x80x94the physical properties of the human body do not change rapidly. For example, the conductivity of the human body tends to be constant and hence it can be used to measure the distance between the occupant and the corresponding protection module through the use of a capacitive sensor.
The present invention provides an occupant proximity sensor utilizing an occupant""s conductivity to determine proximity by measuring the capacitance between the occupant""s head and roof-mounted array of sensors (electrodes).
A transmitting electrode is mounted in a vehicle seat. An array of receiving electrodes is mounted to the ceiling of the vehicle above the occupant""s seat. A control unit serially switches these receiving electrodes to create a profile of the produced electric field. Desired precision is achieved by counting the proximity for each element in the array. The resulting data indicates in two dimensions the accurate position of the occupant in the passenger compartment. The control unit utilizes an excitation method and a synchronous detection method to measure capacitance. It uses micro power low frequency signal that is safe for human.